Reversible Modulation of Thermal Conductivity in GaN via Strain-Driven Reorganization of Dislocation Ensembles

TL;DR

This study demonstrates that applying elastic strain to GaN can reversibly reorganize dislocation ensembles, significantly enhancing thermal conductivity by up to 23%, revealing defect correlations as a tunable factor for heat transport.

Contribution

It introduces a method to reversibly modulate thermal conductivity in GaN through strain-driven reorganization of dislocation ensembles, a novel approach to controlling heat conduction in crystalline materials.

Findings

Reversible 23% increase in thermal conductivity under 0.21% uniaxial strain.

Strain induces a change in dislocation correlations, evidenced by x-ray diffraction.

Phonon linewidth shows a non-monotonic evolution with strain, correlating with thermal conductivity.

Abstract

Crystalline defects are generally regarded as static phonon scatterers that irreversibly suppress thermal transport. Here we show that elastic strain can dynamically and reversibly reorganize dislocation ensembles and strongly modify heat conduction. Using in situ strain-dependent time-domain thermoreflectance measurements, we observe a reversible enhancement of thermal conductivity in GaN by 23% under only 0.21% uniaxial strain. High-resolution x-ray diffraction reveals progressive narrowing of the symmetric (0002) reflection together with a crossover of the diffuse scattering tails from a $q^{-3}$ to a $q^{-2}$ power law, indicating a strain-induced change in the statistical correlations of threading dislocations. Raman spectroscopy further shows a non-monotonic evolution of the $E_{2}^{\mathrm{high}}$ phonon linewidth, with a minimum near the same threshold strain at which thermal conductivity sharply increases. These results support a picture in which elastic strain promotes reversible screening and ordering of long-range dislocation strain fields, thereby reducing phonon scattering. Our work establishes defect correlations as a tunable degree of freedom for controlling thermal transport in crystalline solids.